This general project area has as its objective, to develop and refine methodology for the quantitative and qualitative determination of compounds and classes of compounds of general interest to the Institute and specific interest to individual investigators. Recent work has emphasized development and validation of methods for (a) quantitative and reproducible extraction and clean-up of halogenated aromatic compounds from biological materials for subsequent GC-MS or immunoassay, and (b) fortifying samples under conditions yielding equilibration of "spike" with endogenous compound.